Electrical conductor and a method of making it



C. C. SMITH Oct. 3, 1944.

ELECTRICAL CONDUCTOR AND A METHOD 0F MAKING IT Filed Oct. 5, 1940 $5.5 Robo@ ...mm 29.1@

r M m Tm /T M, A VM W.. m fm c R Patented Oct. 3, 1944 ELECTRICAL CONDUCT 0F MARIN B. AND A METHOD G IT charla;v c. smith, Cranford, N.- J., signor to Western-Electric Company, Incorporated, New York, N. Y., a corporation of New York Application october 5, 1940, serial No. 359,878

4 claims. (c1. 154-225) This invention relates to electrical conductors and a method of making them, and more particularly .to insulated electrical wires and a method of making them.

phone apparatus has a core of copper Wire which' may be a single, solid strand or may consist of a plurality of small strands laid together in parallel relation or intertwisted together or interbraided together. On this core are served, or sometimes .knitted or braided, one or more coverings of silk threads; and one or more coverings of cotton thread are served, or sometimes knitted or braided, over'the silk coverings. The covered wire is then passed through a bath of a liquid preparation .of cellulose acetate or other suitable cellulose ester dissolved in a vehicle comprising acetone as the principal solvent agent. The solvent is then dried out, leaving aprotective lm or coating of cellulose acetate on and sometimes more or less impregnating the outer cotton covering. Insulated wires thus made are found to have eminently satisfactory electrical properties as Well as mechanical strength and resistance to damage. Since the appearance of artificialA silk in commerce, many attempts have been made to substitute artificial silk for real silk in the covering of wire as described. However, most of the artificial silk materials used in commercial threads comprise vesters of cellulose, usually the acetate and sometimes the nitrate, as a principal component, and these are quickly soluble in acetone liquid and also absorb vapors of acetone more or less greedily and soften, melt or dissolve.

electrical conductors havev of the artificial silk coverings keep their individual identity, because of high flexibility and excellent electrical and mechanical properties combined with materially lower cost, as compared with those in which real silk is used, have not been successfully manufactured heretofore.

An object of the present invention is to provide an insulated electrical wire having covering of Icellulose acetate or the like and of artificial silk threads or the like material easilyr damaged by acetone or the like, separated by an intermediate covering of fibers of cotton or other material inert to the solvent action of acetone.

With the above and other objects in view, the invention may be embodied in an insulated electrical conductor wire comprising a conductive core, a covering thereon of fibrous material soluble in acetone or its vapors, a covering thereover of fibrous material inert to acetone and its vapors, and a coating thereon of amorphous cellulose ester material.

A Afurther embodiment of the invention may present a method making such wire which comprises steps of serving, knitting or braiding a covering of threads of textile material soluble in' acetone or its vapors on a w1re, serving, knitting or braiding a covering of threads of textilematerial inert to acetone and its vaporsoverthe said first named covering, extruding a coating of a thickly viscid preparation of cellulose ester softened in acetone over the second named cov- Hence attempts to make such wires as above described with artificial silk replacing real silk in the inner coverings have not been satisfactory. The silk servings, if not wholly destroyed by liquid acetone soaking through the overlying cotton layers from the cellulose acetate in acetone baths, are softened, melted and coalesced more or less, or dissolved by vapors of acetone from'- the same source, especially during stoppages of the apparatus to repair breaks in the wire or to replace empty supply reels therein. Thus wires 'covered with artificial silk and 4with cotton over the silk and with cellulose acetate over the cotton, although. highly desirable when theV threads ering and drying out the acetone.

Other objects and features of the invention will appear from the following detailed descrip-v tion of its embodiment in an insulated wire and a method of making insulated wire, taken in connection with the accompanying drawing, the single figure of which presentsan enlarged diagrammatic view in side elevation of a piece of insulated wire constructed in accordance with the invention.

' As herein disclosed and illustrated in the single figure on the drawing, a wire constructed in accordance with the invention may comprise a conductive core III, a flrst covering II of articial silk on the core, a second covering I2 of artificial silk over the first covering, a third covering I3 of cotton over the second covering, and an outer coating Il of cellulose acetate over the third covering.

Each of the coverings II, I2 and I3 consists essentially of textile threads served, knitted or braided in place bymeans of methods and apparatus too well known to require elucidation or illustration here. In the lspecific case illustrated H, l2 and in the drawing, the covering ii is served with a left hand pitch directly on the bare wire i0; the covering i2 is Vserved with right hand twist directly on the covering il; and the covering I3 is served with left hand twist directly on the covering I2. Each of these coverings is illustrated as served; but any one or two or all three may be knitted or braided if desired. In the actual case used as illustration here, the threads used to form each of lthe coverings il and 02 were of Rayon a commercial artificial silk consisting essentially of cellulose acetate; and the covering i3 was of cotton thread. l

The coating Mis of amorphous cellulose acetate. It is made by extruding over and drying on the covering I3 a coating of an extremely vlscid preparation of cellulose acetate and other solids soitened by being compounded with a solvent consisting essentially of acetone. To illustrate the nature ,of the raw coating material used, a suitable preparation will contain by weight 27% of cellulose acetate and 40% oi' acetone with 31% of other solids (plasticizers, llers etc.) and 2% ci other liquids. Anotherway of describing the essentials of this coating material is to saythat it contains 'I2 ounces of cellulose acetate per gallon of acetone; of thematerial relevant to the present invention are the presence in material amount of acetone which is harmful, whether as liquid or as vapor, to Rayon, and thel high viscosity of the material as used. Measured under ordinary laboratory conditions, the viscosity of this material at 75 F. is about 25,000 poises, while at the extrusion temperature o1' about 105 F. lit is 'about 18,000 poises. A suitable method and apparatus for extruding and drying the coating IB are respectively disposed and claimed in applications Serial Nos'. 209,396 and 295,024, filed respectively on May 21, 1938, and September l5, 1939, both by Edwin E. Newton et al; Application No. 295,024 has matured to Patent No. 2,260,8S0, dated Oct. 28, 1941.

A coating of such material extruded over the covering i 3 forms a tough, amorphous, seamless film entirely covering the covering l@ and more or less bonded into the superficial portion of the covering I3, as indicated at i5, by the extrusion pressure. Due to the volatility oi acetone and the relatively small proportion of it present in the raw coating material, the acetone is evaporated immediately after the raw coated strand leaves the extruding means before enough acetone vapor, much less enough liquid acetone passesl through the coating I3 to cause the threads to adhere together or even coalesce wholly and thereby damage the coverings I2 or il.

Where attempts are made to e'ect the same result' by passing the thread covered strand (i0,

I3) through the liquid bath of cellulose acetate in acetone used in the case oi wire covered with real silk and cotton, it is found that after drying, one or even both ci the coverings ii and I2 may have disappeared entirely, having been extracted by the acetone, on, at best, that their structure has disappeared entirely and they have become so diminished or irregular in thickness as to be worthless in practice. It is only where the cellulcseacetate paste used is so low in acetone relatively to its content of cellulose acetatev that its viscosity is upward of 7,000poises at 75 F. that such coatings can be satisfactorily applied without damage to the lRayon or similar coverings II and I2 under the cotton covering I3. The solutions used for The characterizing featuresl coating real silk covered wire are a totally diierent thing in physical character. Typically they contain onlytwo-iths as much solids in proportion to solvent, and are sirupy, freely owing liquids; whereas the materials herein disclosed are perhaps technically liquid, but are in consistency like very thick warm tar andv cannot be used as a means for coating by dipping.

While the invention is herein illustratively disclosed as embodied in an insulated wire comprising. a covering of mutually wholly independent cellulose acetate nbs-rs and an. outer coating oi amorphous cellulose acetate separated by a covering of eottoniiber, and also as embodied in a method of making such wire which characteristicallyincludes a step of extruding a very viscid preparation of cellulose'acetate in acetone upon the cotton covering to iorm the amorphous coating, it will be clear that the invention is not so limited. An inner coating of cellulose nitrate is as subject to destruction by acetone liquid or vapor as cellulose acetate. So also the acetone ingredient might under some conditions be replaced by another such as toluol, xylol, or the like able to attack the material of factory insulating qualities, this covering might ceptible of attack by the solvent used. v

Rayon -on a wire a covering of threads of cellulose acebe'of Wool or linen or other suitable fiber not sus- 'Ihe embodiments particularly disclosed herein areillustrative and may be modiied and departed from without departing from the spirit and scope of the invention as pointed out in and limited only by the appended claims.

What is claimed is: Y

1. vThe method of making insulated electrical conductor wire which comprises steps of forming on a wire a covering of insulating fibrous material susceptible of attack by the vapors as Well as the liquid form of a specific solvent liquid, forming over the said covering a second covering of insulating fibrous material not susceptible of attack by the said solvent, and extruding upon the outer surface of the said second covering a coating of insulating material softened with an insufcient amount of the said solvent to allow even the vapors of the solvent to penetrate materially through lthe secondcovering to attack the first covering.

2. The method of making insulated electrical conductor wire which comprises steps of forming on a wire a covering of insulating iibrous cellulose ester susceptible of attack by the vapors as well asthe liquid form of a specliic solvent liquid,

lforming over the said covering a second covering of insulating fibrous cellulose not susceptible of attack bythe said solvent, `and extruding upon `the outer surface of the said second covering a 'coating of insulating material softened with an insumcient amount of the said solvent to allow even the vapors of the solvent to penetrate materially through the second covering to attack the iirst covering.

3. 'I'he method of making insulated electrical conductor wire which comprises steps oi forming tate, forming over the said covering a covering of cotton threads, and extruding upon the outer surface or the cotton thread covering a coating of thickly vi'scid material of viscosity not less than-'7,000 poises at 75 l1". and containingcellulose acetate and acetone as its principal ingredients, whereby to leave the cellulose acetate the inner coverings IIv or I2. Furthermore, while the preferred'matethreads substantially unaffected by even the vapors of the acetone.

4. The method of making insulated electrical conductor wire which comprises steps of 'forming on a wire a covering of threads of cellulose acetate, forming over the said covering a covering of cotton threads, and extruding upon the outer surface of the cotton thread covering a coating of thickly viscid material of viscosity of the order of 25,000 poises at, '75 F. and containing cellulose acetate and acetone as its principal ingredients, whereby to leave the cellulose acetate threads substantially unaffected by even the vapors of the acetone. l

CHARLES C. SMITH. 

